Electric motor



C. A. RALL ELECTRIC MOTOR Filed July 24, 1953 nuenZ r (E71 (2 ia/4f M, W' ZUM res UNITED PATENT ..@1.;,;:

attains nrncc Moron Carl A. lhall, Chicago, Hll, assignor to Bodine Electric (Company, Chicago, a cor-paranoia of ois Application July 24., 1933, Serial No. 681,924

3 Ctaima. (Kill. ILiZ- fi'id) This invention relates to new and useful improvements in dynamo-electric machinery and more particularly to self starting single phase motors, mainly and especially those of the induc 5 tion type.

Heretofore and up to the present time, in order to give some degree of rotary eifect to the held and so provide starting torque for such motors, it has been customary to use split-phase starter ill windings'in the case of the larger motors, where a strong starting torque is required; and in the case of smaller motors shading coils have been used.

The main objects of the present invention are id to provide a simpler and better method of obtaining starting torque for single phase induction motors; to provide for increasing the starting torque of such motors of all capacities, and without materially increasing their weight or size and without increasing the cost; to provide a more economical method and means for starting this kind of motor of very small size; to provide a novel and improved form and make-up of field member adapted to enable accomplishment of the foregoing purposes; to provide for this through the use of multiple flux paths of unlike reluctances; and to provide especially for applying this invention to induction motors, though not limited thereto.

Whenever the constantly varying flux created Bil by an alternating current penetrates iron masses or becomes linked with electro-conductive material, power is expended and watt losses mainly in the form of heat are bound to occur. These losses are generally known as iron losms and as secondary or eddy-current losses. High reluctance paths favor small magnetic leg, and low reluctance favors greater lag.

I now refer to the accompanying drawing,

Fig. 1 illustrates a four pole, reversible relucd-ll tance, start motor having a stator of the distributed winding type.

Fig. 2 illustrates a four pole reversible reluctance start motor having a stator provided with distributed windings which may be form wound coils, all of which are energized for either direction of rotation.

' The reversible motor of Big. 1 has a rotor 44 and a yoke 15 slotted to receive windings 4G and ll. The switch 52 serves to reverse the motor.

5%) It is to be noted that on. Fig. 1 windings It include a set of two concentric coils--83 and 84 and two other such coils 35 and t8 disposed &5 therefrom; and that windings il, being 180 from windings 3t, similarly include a set of two concentric coils @l and 88 and two other such coils 8d and till, disposed 45 therefrom; coils 83- and 8% being 180 from coils 8i and 8&3, and coils 85 and 85 being l80-from coils t9 and til.

The said coils are all in slots and the teeth embraced by the, coils are of difierent heights, so 5 that the magnetic reluctance difiers accordingly. When the coils are connected conjunctively the flux change surges in one direction rotatively, and when the coils are connected differentially the flux change surge is in the opposite direction roit) tatively, as indicated on the rotor dd of Fig. l by the full and dotted arrows respectively, by reason of which the motor is reversible, as will be explained more in detail.

The said coils 83 and 9t inclusive are inter-l5 connected as indicated by, dotted lines. When the switch 52 is closed to the left for clockwise rota: tion, as shown in Fig. l, the circuit extends from line conductor at to and over lead 92, and for a moment in the alternating voltage cycle the cur- 2o rent may be said to have instantaneous flow in that direction. Thence the circuit extends to and through coil 85, the said instantaneous flow here assumed being indicated by the conventional circles with dots and crosses showing current ap- 2d proach and retreat respectively, as will be understood. From coililh the circuit goes by lead 93 to coil B6, and thenceby lead 941 to coil 9E3, thence by lead 95 to coil 89, thence by lead 36 to the upper middle contact or hinge post ill of switch 52, so thence by blade 98, assumed to be closed to the left, to switch contact 99, thence by lead Hill to coil 8?, theme by lead Hill to coil 88, thence by lead N32 to coil 8 thence by lead N33 to coil 83, thence by lead ittto switch contact Hi5, thence 35 by blade race to the lower hinge post idl, thence by lead 9% to the'other line conductor I09, as indicated by full arrows.

The result is that coils tit and energized as at the certain instant referred to, tend to cause a north pole at the right side of the lower tooth marked N, and coils 83 and 8t tend to cause a north pole on the left side. The joint effect is a very strong joint north pole at N. But the polar tooth T at the right is shorter than the polar tooth T at the left; wherefore, the pole N builds up quickly but weakly on the right and slowly and strongly on the left, and it weakens and disappears quickly on the right end, slowly on the left. This in magnetic eifect is a leftward movement of the flux on the lower side of Fig. 1. The same is true of the north pole N at the top, except that the movement is toward the right, and so this makes for clockwise field rotation, as indicated by the plain arcuate arrow on the rotor M. It is to be understood that corresponding consequent south poles S of corresponding period are produced midway between the said north poles, at the right and left on Fig. 1. Here the short tooth on one side and the long tooth on the other side of each main south pole tooth also makes for flux rotation, in harmony with the said north polar efiects. In-the next half cycle the current and polarity reverse, but the direction of field rotation stays the same, owing to the fixed relation of the various polar teeth and the exciting coils.

When the switch 52 is closed to the right, for reversing the motor, the current at a given moment, corresponding with that before referred to, fiows from line conductor 9| through the motor and back to the other conductor me, just as above described, except that said switch causes reverse flow through coils 31-, 88, 83 and 86, as indicated by the dotted arrows.

From switch post 91 to post it! this reverse flow may be traced over blade 98, now swung to the right, lead m5, coil 83, lead 803, coil 86, lead M12, coil 88, lead Nil, coil til, lead EBB, post St and blade I06 to post ml.

At this moment the coils 85, 86, Bil and 9b serve to produce north poles as before, but the reversed coils now serve to produce south poles in such manner and place as to push the north poles over somewhat in a counterclockwise direction. As a result of this the effective center of each north -pole is moved from the corresponding tooth marked N to the tooth marked N where, as viewed in Fig. 1, the lower north pole, due to the short tooth at the left and the long teeth at the right, will build up quickly but weakly at the left and slowly but strongly at the right, and this makes for reversal in rotation, of the field flux and the motor, to the counterclockwise direction. The polar shift here referred to also results in south poles at teeth S'S where, as may be noted, the adjacent short and long south pole teeth are so disposed as to assist in the said counterclockwise rotation of field flux.

In Figure 2 the motor includes a rotor H, a

stator yoke ring 12, field coils l3 and on one side, and coils l3 and 14' on the other side, and a reversing switch 15. Here in Fig. 2 the general plan is similar to that of Fig. 1, but somewhat simplified, there being fewer coils and the tooth and slot feature being also much simpler, and there being eight slots and eight teeth. Here each tooth or polar part 16 has a stepped face to vary the reluctance, being low on one side 16' and high on the other side 16". When the coils are connected for combined effect the field, as it varies, rotates in one direction and when the coils are connected for opposing eifect the field rotation is reversed, as will be explained. The slots 11 are here shown of the open type to accommodate form wound coils.

The said coils 13, I4, 13 and 'H' are interconnected as indicated by dotted lines, and directions are indicated by arrows, as in Fig. l.

When the switch 15 is closed to the right, as shown, the current at a given instant flows from line co! ductor I over lead I I2 to coil 13, thence by lead H3 to coil 13, thence by lead I to hinge post N of switch 65, through the upper blade ii to lead ill, thence to coill l, thence by lead M3 to coil i l, thence by lead ilii to the lower switch blade 120 and thence by lead 92! to the other conductor l22 of the line.

The current in flowing thus induces strong instantaneous north poles on the two opposite teeth marked N and corresponding consequent south poles at the teeth marked S; It is to be noted that the stepped feature of the teeth alternates, and that the said teeth N, N and S, S are all stepped in the same direction; that is to say in the clockwise direction for inward height toward the rotor. Now, as the flux builds up quickly and weakly on the short side it and quickly and strongly on the tall side it", the magnetic result is clockwise swing or rotation of the field flux, which causes the rotor to rotate accordingly, as indicated by the full curved arrow.

When switch l5 is swung over to the left, reversal of current is efiected in the coils M and M, as indicated by the isolated dot and cross marked circles in corresponding stator slots. This flow of current instantaneously results in coils l3 and I3 tending to build up poles at the slots lying axially of said coils; and likewise coils i l and 16, carrying reversed current, tend to build up south poles at slots lying axially of said coils. But mutual reaction tending to equalize spacing of the poles results in north poles being induced actually at teeth N and N and south poles at teeth S and S. Now the sequential stepping of the effective poles isreversed to counterclockwise, with resultant reversal of flux rotation and so also reversal of the motor.

It is to be understood that some of the details set forth may be altered or omitted without departing from the spirit of the invention as defined by the following claims:

I claim:

1. A reluctance start motor having field wind-' ings arranged in two sets, one set being reversible to control the direction of field flux rotation, the windings for each pole being distributed and arranged to overlap mutually.

2. In a reluctance start motor, a slotted field ring having exciter windings distributed in its slots to produce poles, said windings for each pole com- I prising two over-lapping diverse inductance sets of coils distributed with the polar axis of one set displaced somewhat circumferentially from the axis of its mate to produce rotary field movement, and switching means arranged and connected to render one set reversible electrically with respect to the other whereby the motor is reversible.

3. In a slotted field ring member of a reluctance start motor, a long-toothed part and a shorttoothed part disposed adjacently to serve as a polar element, in combination with a highly inductive slot-winding disposed to excite the said long-toothed part, and a lowly inductive slotwinding disposed to excite said short-toothed part, said windings being mutually ofiset axially but somewhat overlapping each other, and means to reverse the relative connection of said windings, for reversal of the motor.

CARL A. RALL. 

